Various types of chemical analyses have been used in the detection and measurement of various components of clinical interest in biological fluids. These analyses can be conveniently divided into two categories which are commonly labelled wet chemistry and dry chemistry. The wet chemistry analyses employ reagents in liquid solution and are widely used in both manual and automated analysis methods. The dry chemistry analyses employ reagents in substantially "dry-to-the-touch" test devices. Although both types of analyses have their advantages, the dry chemistry methods often are simpler in design, require less reagent manipulation, give quicker results and are more stable. Many dry chemistry methods have the disadvantage of being only qualitative, or, at best semi-quantitative, in their response to a given concentration of analyte, the compound to be measured in the biological fluid.
Several dry chemistry test devices which are capable of quantitative results have been described. In U.S. Pat. No. 4,042,335, issued to Clement on Aug. 16, 1977, a multilayered device for the analysis of liquids is described. The device includes (1) a reagent layer including a composition that is interactive in the presence of a predetermined analyte to provide a diffusible, detectable species, and (2) a registration layer that is permeable to the detectable species and within which such species can be detected. The element can include other layers which provide the radiation-blocking and for uniform spreading of the test sample. This test device can be used in the quantitative or qualitative analysis of biological fluids. However, the operational flexibility of this test device is severely limited: once liquid is applied, uncontrollable processing occurs by diffusion through the various layers. No means to control this diffusion is provided.
In U.S. Pat. No. 4,144,306, issued to Figueras on Mar. 13, 1979, a similar multilayered test device is disclosed. This test device can be used for immunochemical analysis. The layers can be spaced apart. Immediately after the test sample is applied, a compressive force can be applied to allow fluid contact among the previously separated layers. This test device provides no control of analyte or reagent migration through the layers after the sample is applied and the layers contacted.
U.S. Pat. No. 3,723,064, issued Mar. 27, 1973 to Liotta, describes a layered testing device for quantitatively determining the concentration of an analyte which includes a first or receiving layer impregnated with a chemical reagent for reaction with the analyte by which an end product is produced, a second or transmission layer to draw the end product through a porous membrane separating the first and second layers, and a third or indicator layer impregnated with reagents capable of reacting with the end product to provide a visual indication of the presence of the end product generated in layer one and reaching layer three. The indicator layer can be adapted to be peeled off and saved to provide a permanent record of the test. The porous mebrane interposed between the first and second layers has regions of different permeability which permit passage of the end product according to the concentration of the analyte. Passage of fluid through the porous membrane is solely a function of concentration of the analyte and is not otherwise controllable.
U.S. Pat. No. 4,258,001, issued Mar. 24, 1981 to Pierce et al., describes a multizone element for the analysis of substances in liquids which contains at least two permeable zones in direct fluid contact. No means are provided for controlling the diffusion of substances between zones after sample application.
U.S. Pat. No. 4,166,093, issued Aug. 28, 1979 to Smith-Lewis et al., describes an element for the analysis of liquids which contains a radiation-transmissive, detectable species migration-inhibiting layer interposed between a porous radiation-blocking layer and a radiation-transmissive reagent layer. All three layers are permeable to the analyte of interest. The migration-inhibiting layer acts solely to reduce the migration of the detectable species back into the radiation-blocking layer where it would be undetectable. That is, it functions as a one-way valve.
European Patent Application 0,046,004, published Feb. 17, 1982, describes a nonchromatographic assay device for the determination of members of an immunological pair. The device consists of at least two layers, an immunosorbing zone and a liquid absorbing zone in a liquid-receiving relationship. Additional layers can be involved which serve as barriers to inhibit migration of components of the signal producing system from the lower to the upper layer. The barrier is a chemical or enzymatic barrier and its structural integrity is not breached in the course of the assay.
European Patent Application No. 0,066,648, published Dec. 15, 1982, describes a dry-chemistry multilayer analysis element in which a competitive immune reaction is utilized for the detection of a specific component. One of the layers can be a timing layer, the function of which is to retain a sample solution in the reaction layer for a time sufficient to allow complete reaction of the sample with the detection reagents. The timing layer is typically composed of a polymeric material, preferably gelatin. It does not function as an all-or-none barrier to liquid flow, but merely controls the rate of that flow.
The multi-layered test devices described above share a common deficiency: Once the test sample is applied, the migration of analyte, reagents and reaction products becomes uncontrollable. The ability to migrate as well as the rate of migration are functions of the structure of the device. There is no way to (1) stop the migration of a particular species within a preselected layer of the device for the purpose of increasing the reaction time within that particular layer and (2) restart the migration into subsequent layers.
There is a need for a multilayered test device for chemical analysis in which one or more of the layers provides a means to stop or start the analyte and/or reagent migration through the layers once the test sample has been applied.